1. Field of the Invention
The present invention relates particularly to a steering device in an outboard motor.
2. Description of the Related Art
As a mainstream propulsion engine or a propulsion system of a craft or a boat, there are outboard motor, an inboard-outdrive motor, an inboard motor, and so on. The outboard motor among these is called an outboard drive or the like, and is integrally constituted with an engine, an auxiliary machine or the like thereof, a gear or a shaft of a driving system, a screw, and so on, and in general, is mounted on a transom board at a stern of a hull. The outboard system is typically mounted on a small-sized boat or the like, and has a steering function and a tilting function.
Further, the inboard-outdrive motor is called an inboard engine outboard drive or the like, as an installation method of a propulsion engine of a small-sized craft or the like, and an engine is mounted on an inboard stern portion and a drive unit made by integrating a reduction gear, a forward/backward clutch, a propeller, and so on is disposed in the exterior.
When such a boat actually travels on sea or on water, steerage is quite important, and various measures are taken in a steering device for steering. For example, a conventional outboard motor is fixed to a hull with a pair of clamp bracket portions, and a swivel bracket is supported between the clamp brackets via a through tube (tilt shaft). An outboard motor main body steers centering on a steering shaft on the swivel bracket. At a time of steering, a lift force (steering force) occurs in a lateral direction, and this force is transmitted to the hull via the clamp bracket.
Further, in a conventional small-sized outboard motor, a driving shaft and a steering shaft are matched. Therefore, a large steering angle can be set as a steering angle and is able to be steered, and in some cases steering of 360 degree is possible.
Further, in a conventional inboard-outdrive motor, a tilt shaft and a steering shaft are placed in a center of a universal joint of a drive shaft.
Further, a conventional method called sea drive is known and can achieve a large steering angle by mounting an outboard motor of large output on a swivel bracket in a manner to match a steering shaft and a drive shaft.
Further, a conventional form called POD is know, in which a drive shaft and a steering shaft match, and thus a large steering angle can be achieved, usually enabling a steering angle of about 360 degrees.
However, in the conventional outboard motor, the clamp brackets are fixed to the hull in a cantilever manner. Thus, at a time of trim movement (tilt), since a lift force (steering force) center comes away from the hull to the rear, the clamp brackets becomes open in a shape of separated “V”. There has been a problem that an outboard motor cannot generate a large lift force (steering force) for the above reason. Further, there has been a problem that a trim (tilt) angle cannot be made large in a state of thrust. Further, there has been a problem that steering does not work well for a similar reason, leading to a poor performance of turning in a small radius.
Further, in the conventional small-sized outboard motor, an engine is mounted on a steering shaft receiving portion, and more concretely, a mount gum thereof is in an outer side of the steering shaft receiving portion. Thus, there has been a problem that engine vibration is easy to be transmitted to a hull. Further, since a span of a steering shaft receiver is short, the outboard motor can withstand a small propulsion force but cannot be applied to a large propulsion force as in a case of a large-sized outboard motor or the like.
Further, in the conventional inboard-outdrive motor, since a bending angle of the universal joint is limited, a tilt angle and a steering angle are smaller than those of an outboard motor. Therefore, there has been a problem that steering does not work well, leading to a poor performance on turning in a small radius.
Further, in the conventional method called sea drive, since an outboard motor engine part is positioned low in relation to a water surface, there is a problem that the engine is easy to be wetted, making it hard to keep reliability and corrosive resistance. Further, since the tilt shaft is positioned apart from a gravity center of the outboard motor, a large tilt device is necessary or an inertial mass is large, and thus there has been a problem that a large impact force occurs at a time of collision with a driftwood or the like.
Further, the above-noted conventional method is exclusive to a large-sized craft for which shallows are not taken into consideration, and there has been a problem that if the method is to be applied to a boat, the boat is largely damaged at a time of collision against an obstacle (including a seafloor) since there is no impact absorbing mechanism.
Further, in an outboard motor or the like of this kind, since a drive shaft and a steering shaft are matched, a large steering angle can be obtained, but because of the fact that a lift force (steering force) is supported by a gimbal surface (a mounting surface to a transom board) apart from the steering shaft, a large steering force cannot be given, resulting in a problem that high-speed turning in a small radius is not possible.
Further, since the steering shaft and the drive shaft match, the large steering angle can be given, but since the steering shaft (drive shaft) is not orthogonal to a traveling direction of a boat, a lateral direction component of the steering force is small and high-speed turning is not possible.
Further, since the engine is disposed at a high position and thus is advantageous in view of being wet, and in some cases mounting thereof on the hull is as simple as mounting of an outboard motor, but since the drive shaft is universally joined, there is a problem that neither a steering angle nor a tilting angle can be taken large.